Preheated fuel and oxidant combustion burner

ABSTRACT

A burner apparatus comprises a conduit adapted to convey preheated oxidant and having outlet and inlet ends, and a conduit adapted to convey preheated fuel and having outlet and inlet ends. The conduit adapted to convey preheated fuel is substantially parallel to the conduit adapted to convey preheated oxidant. The conduit adapted to convey preheated oxidant is positioned substantially vertically above the conduit adapted to convey preheated fuel. The conduit adapted to convey preheated oxidant and the conduit adapted to convey preheated fuel each are positioned within its own respective elongate cavity in a refractory burner block. Each of the conduits are positioned in their respective cavity such that a substantially annular region is present between an outer surface of each conduit and its respective cavity. Each conduit inlet end extends through a respective plenum for receiving an ambient temperature fluid, the plenums adapted to pass the ambient temperature fluid into the respective annular regions.

This application is a continuation of U.S. application Ser. No.09/637,295, filed Aug. 11, 2000 now abandoned, the entire contents ofwhich are incorporated herein by reference which is a continuation ofSer. No. 09/338,844 filed Jun. 23, 1999, now U.S. Pat. No. 6,126,438.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to apparatus for combusting preheated fuel and/orpreheated oxidant.

2. Related Art

There are three basic types of combustion systems based on temperatureof the fuel and oxidant: First and most common burner system utilizeunheated (or ambient) fuel and oxidant for combustion. Both air-fuel andoxy-fuel burners of above types are widely used in industry (see U.S.Pat. Nos. 5,199,866; 4,690,635).

The second type of burner system employs preheating the ambient fluids(fuel and oxidant) inside the burner embodiment. This method employsambient or slightly preheated fuel and oxidant as an input to theburner. It is commonly used with air-fuel burners and combustionengines. U.S. Pat. No. 4,257,762 describes one such method wherepreheated forced draft air is used for preheating fuel gas by partialmixing in the burner passage. In another application (U.S. Pat. No.5,413,477), hot flue gas is entrained inside the burner to preheat fueland combustion air using fuel-rich and fuel-lean staged combustion. Onoxy-fuel combustion systems, the concept has been adapted and thepreheating of natural gas is used by mixing with another hot fluid, orpartial combustion in an oxygen poor atmosphere that leads to sootformation as well as preheating (U.S. Pat. No. 5,725,366). These areknown technologies where preheating of either oxidant or fuel is carriedout within the burner body or burner block. In summary, the burner orburner block is used as a heater for fuel, oxidant or both. In the firststage, partial combustion of fuel with oxidant is carried out and in thesecond stage, subsequent mixing of hot combustion products from firststage with the remaining fuel and oxidant is carried out. Thus, overallpreheating of fuel and oxidant is achieved.

Preheated air for air-fuel burner systems is known. However, mostapplications involve preheated combustion air (U.S. Pat. No. 4,492,568;U.S. Pat. No. 5,823,769). The traditional methods employ a refractoryheat exchanger (two regenerators) to preheat combustion air in a cyclicmanner. Thus, with air-fuel burners and ceramic regenerators, preheatingtemperatures as high as 1100° C. for air containing 21 (volumetric)percent oxygen is quite common. The air is preheated in such devices byperiodic (or cyclic) flow through a given regenerator (such as checkerscontaining ceramic elements) that have been preheated by the hot fluegases during the previous cycle. The disadvantage of above heat recoverysystem is that it can not utilize pure oxygen. The first reason issafety related. The flue gas-leaving the furnace is usually dirty due toentrained process particulates, fuel, condensate and vapors, which candeposit on the heated checker surfaces in one cycle and then reactreadily with preheated oxygen in the next cycle. This may createexplosive conditions. The second reason is due to slippage of preheatedoxygen (precious commodity) through refractory cracks and joints of theregenerator structure.

The use of metallic recuperators is also widespread but the preheattemperatures are lower than 700° C. due to the metallic construction andcorrosion effects of hot oxidant (air) and flue gases on the metallicparts of the recuperator. Yet these kinds of air-fuel heat recoverysystems have lower thermal efficiency due to the nitrogen contained inthe air. This inert nitrogen has to be heated to process temperature andthis heat is simply wasted. In addition, nitrogen at high temperaturetriggers the forming of NOx.

The preheated oxygen for combustion has been used before in the case ofa reforming reactor (U.S. Pat. No. 5,588,974) where oxygen and steam areused to transform hydrocarbons into hydrogen and carbon monoxide. Thehot oxidizing mixture is fed into the reactor at temperatures rangingfrom 500° F. to 1200° F. The object was to reform fuel into H₂ and CO bypartial combustion. The combustion was not carried out in stoichiometricproportions to release heat for heating applications such as steelmelting, glass melting, heat treatment, etc. The objective of thepresent invention is different since it deals with a combustion burner,where fuel is combusted with oxygen in nearly stoichiometricproportions.

SUMMARY OF THE INVENTION

In accordance with the present invention, burners are described whichovercome many of the shortfalls of the previously known burners. Burnersof the present invention are directed to apparatus for producing andoxidant-fuel flame with previously preheated oxidant and/or previouslypreheated fuel (preferably natural gas) for high temperature heatingapplications.

Thus a first aspect of the invention is a burner apparatus comprising:

a) a conduit adapted to convey preheated oxidant and having outlet andinlet ends;

b) a conduit adapted to convey preheated fuel and having outlet andinlet ends, the conduit adapted to convey preheated fuel beingsubstantially parallel to the conduit adapted to convey preheatedoxidant, the conduit adapted to convey preheated oxidant beingpositioned substantially vertically above the conduit adapted to conveypreheated fuel;

c) the conduit adapted to convey preheated oxidant and the conduitadapted to convey preheated fuel each positioned within its ownrespective elongate cavity in a refractory burner block, each of theconduits positioned in their respective cavity such that a substantiallyannular region is present between an outer surface of each the conduitand its respective cavity; and

d) each conduit inlet and extending through a respective plenum forreceiving an ambient temperature fluid, the plenums adapted to pass theambient temperature fluid into and through the respective annularregions.

Preferred are burners in accordance with the first aspect of theinvention wherein the outlet end of each cavity is co-terminous with ahot face of the refractory burner block. Also preferred are burners inaccordance with the first aspect of the invention wherein a plurality ofconduits adapted to convey preheated oxidant are positioned inrespective cavities in the refractory burner block, and plurality ofconduits adapted to convey preheated fuel are positioned in respectivecavities in the refractory burner block.

Further preferred are burners in accordance with this first aspect ofthe invention wherein the outlet end of the conduit adapted to conveypreheated oxidant is connected to an inlet of a preheated oxidant nozzleassembly, the preheated oxidant nozzle assembly comprising an expansionjoint which connects an inlet of the preheated oxidant nozzle assemblyto a preheated oxidant nozzle downstream of the expansion joint, thepreheated oxidant nozzle having a preheated oxidant nozzle outlet and anaxis. More preferably, burners in accordance with this aspect of theinvention are those wherein the preheated oxidant nozzle outlet isrecessed from the outlet end of the cavity in which is positioned theconduit adapted to convey preheated oxidant.

Preferred burners in accordance with this aspect of the invention arethose wherein the outlet end of the conduit adapted to convey preheatedfuel is connected to an inlet of a preheated fuel nozzle, the preheatedfuel nozzle having a preheated fuel nozzle outlet and an axis; thoseburners wherein the preheated oxidant nozzle axis is angled toward thefuel nozzle axis; and burners wherein the preheated fuel nozzle outletis recessed from the outlet end of the cavity in which is positioned theconduit adapted to convey preheated fuel.

Further preferred burners in accordance with this aspect of theinvention are those wherein the cavity in which is positioned theconduit adapted to convey preheated fuel comprises an expansion section,the expansion section connecting a first ambient fuel cavity positionedupstream of the expansion section with a second ambient fuel cavitypositioned downstream of the expansion section and having an internaldiameter greater than an internal diameter of the first ambient fuelcavity, the expansion section having an inlet and an outlet, the inletof the expansion section having a diameter less than the outlet of theexpansion section. Preferred expansion sections are frustoconical inshape.

Preferred burners are those wherein the preheated fuel nozzle outlet ispositioned coterminous with the inlet to the expansion section.

Also preferred are those burners in accordance with the first aspect ofthe invention wherein the conduit adapted to convey preheated fuelextends through and is positioned within an intermediate conduit, theintermediate conduit positioned between the conduit adapted to conveypreheated fuel and its respective cavity. The intermediate conduit hasan outlet and an inlet end, the intermediate conduit inlet and connectedto one of the plenums adapted to receive ambient fuel. The intermediateconduit and the cavity define an annular region between the intermediateconduit and the cavity, allowing for introduction of ambient oxidant inthat annular region, the intermediate conduit and the conduit adapted toconvey preheated fuel creating an inner annular region for conveyingambient fuel.

Other preferred burners in accordance with the first aspect of theinvention are those further including a fluid connection which connectsthe cavity in which the conduit adapted to convey preheated oxidant ispositioned with the cavity in which the conduit adapted to conveypreheated fuel is positioned. This fluid connection allows ambientoxidant to mix with ambient fuel, and provides certain safety features,as more fully detailed herein. Yet another preferred variation of theburner in accordance with the first aspect of the invention is whereinthe fluid connection has a fluid connection inlet and a fluid connectionoutlet, the fluid connection inlet connected with the cavity in whichthe conduit adapted to convey preheated oxidant is positioned at aposition upstream of a point where the fluid connection outlet isconnected to the cavity in which is positioned the conduit adapted toconvey preheated fuel. Preferred burner constructions for this aspectinclude those wherein the refractory burner block is comprised of anupper refractory burner block and a lower refractory burner block, theupper and lower refractory burner blocks contacted in a plane which isgenerally parallel with an axis of the conduit adapted to conveypreheated fuel, the lower refractory burner block having positionedtherein the cavity in which is positioned the conduit adapted to conveypreheated fuel, and the upper refractory burner block having positionedtherein the cavity in which is positioned the conduit adapted to conveypreheated oxidant.

A second aspect of the invention is a burner apparatus comprising:

a) a refractory burner block having a hot face and a cold face, therefractory burner block having an inner surface defining a hollow volumeextending from the cold face to a position intermediate to the cold faceand the hot face within the refractory burner block, the intermediateposition defined by a wall portion of the inner surface of asubstantially solid portion of the burner block, the substantially solidportion having a cavity adapted to convey ambient oxidant extending fromthe wall to the hot face and adapted to have positioned therein aconduit adapted to convey preheated oxidant from the cold face to thehot face, the burner further having a cavity extending from the coldface to the hot face and adapted to receive the conduit adapted toconvey preheated fuel from the cold face to the hot face;

b) the burner further comprising a metallic fluid flow assembly, themetallic fluid flow assembly comprising a first metallic conduit, thefirst metallic conduit adapted to convey ambient oxidant through a firstannulus defined by an inner surface of the first metallic conduit and anouter surface of said conduit adapted to convey preheated oxidant, thefluid flow assembly further comprising a second metallic conduit, thesecond metallic conduit adapted to convey ambient fuel through a secondannulus defined by an inner surface of the second metallic conduit andan outer surface of the conduit adapted to convey preheated fuel, thefluid flow assembly including a connecting metallic conduit whichconnects the first and second metallic conduits, the connecting metallicconduit adapted to convey ambient oxidant from the first annulus intothe second annulus.

Preferred burners in accordance with this aspect of the invention arethose wherein the conduits adapted to convey preheated oxidant andpreheated fuel are both metallic and are both removable from the burnerapparatus.

A third aspect of the invention is a burner apparatus comprising anupper refractory burner block and a lower refractory burner block, andfurther comprising:

a) a conduit adapted to convey preheated oxidant and having outlet andinlet ends;

b) a conduit adapted to convey preheated fuel and having outlet andinlet ends, the conduit adapted to convey preheated fuel beingsubstantially parallel to the conduit adapted to convey preheatedoxidant, the conduit adapted to convey preheated oxidant beingpositioned in the upper refractory burner block and substantiallyvertically above the conduit adapted to convey preheated fuel which ispositioned in the lower refractory burner block;

c) the conduit adapted to convey preheated oxidant positioned within itsown elongate cavity in the upper refractory burner block and the conduitadapted to convey preheated fuel positioned within its own respectiveelongate cavity in the lower refractory burner block, each of saidconduits positioned in their respective cavity such that a substantiallyannular region is present between an outer surface of each said conduitand its respective cavity;

d) each conduit inlet end extending through a respective plenum forreceiving an ambient temperature fluid, the plenums adapted to pass saidambient temperature fluid into the respective annular regions,

e) with the provision that the conduit adapted to convey preheated fuelextends almost entirely the length of the refractory block to anexpansion point which is machined into the refractory burner block lowersection, and a passage adapted to flow at least a portion of saidambient oxidant there through is provided, the passage positioned togive a substantial tangential-axial momentum to the ambient oxidant tocause it to swirl in the ambient fuel cavity, causing delayed combustionof the ambient fuel and preheated fuel.

The invention will be further described with reference to the followingbrief description of the drawing figures, and the description ofpreferred embodiments. Neither the figures nor the detailed descriptionare meant to be limiting or to scale, bur rather should be viewed asaids to the skilled artisan to make and use the inventive burners asclaimed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates in side elevation view one embodiment of a burner ofthe present invention;

FIG. 2 illustrates in side elevation view a second burner embodiment inaccordance with the invention;

FIG. 3 illustrates in side elevation view a third burner embodiment inaccordance with the invention;

FIG. 4 illustrates in side elevation view a fourth burner embodiment inaccordance with the invention;

FIG. 4A illustrates in front elevation view the fourth burner embodimentof FIG. 4;

FIG. 5 illustrates in side elevation view a preferred refractory burnerblock useful in the fourth burner embodiment of FIG. 4 in accordancewith the invention;

FIG. 5A illustrates in front elevation view the refractory burner blockof FIG. 5;

FIG. 6 illustrates in side elevation view a refractory burner blockuseful in a fifth burner embodiment of the present invention;

FIG. 6A illustrates in front elevation view the refractory burner blockof FIG. 6;

FIG. 7 illustrates a side elevation view of a refractory burner block ofa sixth burner embodiment of the present invention; and

FIG. 7A illustrates in front elevation view the refractory burner blockillustrated in FIG. 7.

FIG. 8 illustrates advantages of the concentric nozzle design used invarious embodiments.

DESCRIPTION OF PREFERRED EMBODIMENTS

In accordance with the present invention, combustion burners arepresented which operate preferably with low oxidant supply pressure,such as the pressure delivered by a vacuum swing adsorption oxygenproduction unit. Low oxidant pressure means a pressure ranging fromabout 105,000 to about 170,000 Pa (absolute pressure) (50 m bar to 0.7bar/relative pressure). However, this does not mean that oxidantssupplied via membrane separation, adsorption, absorption, filtration,and the like, cannot be used. Vaporized oxidant may also be employed, asfrom liquid oxygen delivered via tank truck, or via pipeline. Methods ofproduction, transportation, and delivery of oxidants, such as variouspurities of oxygen separated from air, are known in the industrial gasart, and are not part of the present invention. Therefore, these methodsof production, transportation, and delivery are merely noted in passing.

According to the present invention, the fuel and the oxidant areintroduced in the furnace through separate cavities in the burnerassembly. The term “fuel,” according to this invention, means, forexample, methane, natural gas, liquefied natural gas, propane, atomizedoil or the like (either in gaseous or liquid form) at either roomtemperature (about 25° C.) or in preheated form. The term “oxidant,”according to the present invention, means a gas with an oxygen molarconcentration greater than 21%, more preferably at least 50%. Suchoxidants include oxygen-enriched air containing at least 50% vol.Oxygen, such as “industrially” pure oxygen (99.5%) produced by acryogenic air separation plant, or impure oxygen produced by a vacuumswing adsorption process (about 88% vol. O₂ or more, or impure oxygenproduced from air or any other source by filtration, adsorption,absorption, membrane separation, or the like. The term “ambient” as usedherein means the temperature of the surrounding air typically rangingfrom about 0° C. to about 30° C., depending on the locale and time ofthe day, month, and year.

The cavities, as defined herein, are passages through a refractory blockor through a furnace wall, and preferably have a generally cylindricalcross section. Any equivalent cross section can be used, such as square,rectangular, ellipsoid, oval, and the like.

Conduits are defined herein as tubular members having an outer shape,which may or may not correlate with its respective cavity, and which canbe placed in its respective cavity to convey preheated fluids throughthe refractory burner block. Separate conduits are provided, eachadapted to convey either preheated oxidant or preheated fuel. Theconduits can be metallic tubes, metallic tubes or pipes with ceramicends, ceramic tubes, or a combination thereof. Examples of suitableceramic materials for injector tubes include alumina, zirconia, yttria,silicon carbide, and the like. Various stainless steels may be used forthe conduits if the conduits are metallic, and metallic conduits havingheat-protective refractory coatings, employing materials such as thosementioned for ceramic conduits, are also possible.

The conduits adapted to convey preheated fluids are installed incavities opened through the furnace walls, or through a refractory orceramic brick mounted in the furnace wall. In some embodiments, thelength of the conduit is purposely made insufficient to span therespective length of its cavity in the burner block: the preheated fuelor oxidant flows from the conduit into its respective cavity, then fromthe cavity into the combustion chamber of the furnace. Thus, in someembodiments, the conduits adapted to convey preheated fluids stop beforeany change in direction of the preheated gas flow that can be impartedby the geometry of the cavity; in other embodiments, the conduitsadapted to convey preheated fluids may be co-terminous with theirrespective cavity on a hot face of the refractory burner block (the faceof the refractory burner block facing the combustion chamber).

The preheated fuel injection is preferably made by one or more,preferably identical conduits, the conduits in turn positioned withinrespective cavities for conveying ambient fuel, the cavities located ina lower half of the refractory burner block when viewed in sideelevation. Each conduit has an axis, and when there are two or moreconduits for conveying preheated fuel, they are preferably located inthe same plane, which is preferably parallel to a surface of a load inthe combustion chamber, such as a molten glass bath. Ambient fuel issupplied around the (or each) conduit adapted to convey preheated fuel.The ambient fuel can be the same or different composition than thepreheated fuel. Indeed, the composition of each preheated fuel (in caseswhere there are more than one conduit adapted to convey preheated fuel)can be the same or different. For example, for a burner of the inventionhaving two conduits adapted to convey preheated fuel, and theirrespective cavities for conveying ambient fuel, there could by fourdifferent fuel compositions.

The preheated oxidant injection is also preferably made by one or more,preferably identical conduits, the conduits in turn positioned withinrespective cavities for conveying ambient oxidant, the cavities locatedin an upper half of the refractory burner block when viewed in sideelevation. Each conduit adapted to convey preheated oxidant has aninitial axis orientation, and when there are two or more conduits forconveying preheated oxidant, the conduits are preferably located in thesame plane. In one embodiment of the present invention, the conduitsadapted to convey preheated oxidant (and their respective cavities) areessentially parallel with the conduits adapted to convey preheated fuel(and their respective cavities), with no change in direction. However,it is preferably that the conduits adapted to convey preheated oxidant,and their respective cavities, have an initial orientation parallel tothe fuel conduits, and then angle toward the fuel conduits at an angel“A”, as described in more detail herein. The transition between initialorientation and second, angled orientation, is preferably accomplishedusing a nozzle assembly. The nozzle assembly preferably includes anexpansion element and a preheated oxidant nozzle. Ambient oxidant issupplied around the (or each) conduit adapted to convey preheatedoxidant. The ambient oxidant can be the same or different compositionthan the preheated oxidant. Indeed, the composition of each preheatedoxidant (in cases where there are more than one conduit adapted toconvey preheated oxidant) can be the same or different. For example, fora burner of the invention having two conduits adapted to conveypreheated oxidant, and their respective cavities for conveying ambientoxidant, there could be four different oxidant compositions.

The fuel and oxidant exit from the refractory burner block via outletsthat are physically separated (except in certain embodiments describedherein) and geometrically arranged in order to impart to the fuel fluidstreams and the oxidant fluid streams angles and velocities that allowcombustion of the fuel with the oxidant in the combustion chamber.

In preferred embodiments, the fuel cavities do not diverge, but ratherare parallel as the fuel enters the combustion chamber. The same is truefor the oxidant cavities.

The distance 1 between the extremities of the cavities when the fuelenters the combustion chamber of the furnace is comprised preferablybetween about 4 and 10 times the inner diameter d_(f) of each fuelconduit. When the fuel conduit or cavity is not circular, the dimension“d_(f)” is an equivalent or average diameter corresponding to thecross-sectional area of an equivalent circular conduit or cavity.

The various mechanical details of some of the preferred embodiments arebetter understood with reference to the drawing FIG.s.

FIG. 1 illustrates many of the features of the first embodiment of theburner apparatus of the present invention. Illustrated at 2 is theburner apparatus, having a refractory burner block 4. Refractory burnerblock 4 comprises an upper cavity 6 which serves as the cavity throughwhich ambient oxidant, designed as “AO”, passes through on its waytoward the furnace. Cavity 8 (illustrated in the lower portion of therefractory burner block) entails a passage through which ambient fuel(designated as “AF”) passes as indicated by the arrow in FIG. 1. A firstportion of cavity 6 is shown at 10 having a diameter, which is aninitial diameter smaller than the rest of cavity 6. An expansion sectionat 11 is also indicated which transitions the smaller diameter section10 into the main portion of cavity 6. The larger diameter section isdesignated 12 in FIG. 1. Preheated oxidant (indicated as “HO” in FIG. 1)is illustrated emanating on the left-hand side of the burner block at14, while ambient oxidant emanates in the surrounding area as designatedat 16. Both ambient oxidant and preheated oxidant emanate from burnerblock 4 through a hole 18 in the hot face of burner block 4. On thelower portion of FIG. 1, preheated fuel, designated “HF” is indicatedemanating centrally through lower cavity 8 from burner block 4.Preheated fuel 20 is surrounded by ambient fuel, designated “AF” at 22.Both heated fuel and ambient fuel emanate from refractory burner block 4at an exit hole 24 in the hot face of the burner block, which is alsothe terminal point of cavity 8.

Preheated oxidant emanates from burner block 4 having a central axis 26.Preheated fuel emanates from burner block 4 having a central axis 28.Central axis 26 of the preheated oxidant and central axis 28 of thepreheated fuel make an angle “A” as indicated in FIG. 1. Angle Apreferably ranges from 0° to about +20°.

Cavity 8 includes an expansion section 30, and a substantiallycylindrical section 31. Preheated oxidant enters burner apparatus 2through an inlet conduit indicated at 32, while preheated fuel entersburner apparatus 2, at an inlet conduit 34. Preheated oxidant andpreheated fuel are typically and preferably provided by an upstream heatexchanger for each stream, neither of which is indicated in any of thedrawing figures herein. While inlet conduits 32 and 34 are showngenerally cylindrical and parallel, this is not necessarily required inthe practice of the present invention.

A conduit 36 adapted to convey preheated fuel is indicated in FIG. 1positioned generally centrally in cavity 31. Conduit 36 adapted toconvey preheated fuel terminates with a nozzle 38, which is shown as aconverging nozzle. Note that in this preferred embodiment, the terminalpoint of nozzle 38, in the direction of flow, coincides with thebeginning of the expansion chamber 30 of the ambient fuel cavity.

Preheated oxidant enters through conduit 32, and traverses through aconduit adapted to convey preheated oxidant, indicated at 40. Conduit 40in turn connects to an expansion joint or bellows 43, and into a secondportion 42 of the preheated oxidant conduit. Section 42 in turnterminates with a nozzle 44. The terminal point of nozzle 44 is recesseda distance L_(o) from the hot face of burner block 4, while the tip ofnozzle 38 is recessed a distance L_(f) from the hot face of burner block4.

FIG. 2 illustrates a second embodiment burner apparatus at 50. Therefractory burner block 4 is for the most part the same as therefractory burner block 4 indicated at FIG. 1. Furthermore, in thisapparatus, the conduit adapted to provide heated oxidant and itsrespective cavity are essentially the same as indicated in FIG. 1 andthe details are eliminated in FIG. 2 for the purpose of clarity. Ambientoxidant enters into inlet conduit 46 and into a plenum 47, whichconnects, to a converging section 49. The main difference in theembodiment in FIG. 2 from that of FIG. 1 is the provision of ambientoxidant in a plenum 37 at a converging section 39 which leads intorefractory burner block 4. In this embodiment, preheated fuel enters theapparatus at 34 and traverses through a central conduit that is the sameas conduit 36 in FIG. 1, having the same nozzle 38. Preheated fuelenters the apparatus at 34 while ambient fuel enters the apparatusthrough a plenum 35. Plenum 35 connects to an intermediate conduit thatis positioned intermediate cavity 31 and the conduit adapted to conveypreheated fuel 36. This intermediate conduit is designated as 36 a inFIG. 2. Other than these differences, the embodiment is the same as theembodiment in FIG. 1. The angle between the preheated oxidant axis 26and the preheated fuel axis 28 is also designated as angle A in thisembodiment, and may have the same range as in the first embodiment.

FIG. 3 illustrates a third embodiment of the inventive burner apparatus.This embodiment is designated as 60 in FIG. 3, and includes theprovision of a connecting passage 62 which connects the ambient oxidantcavity 11 with the ambient fuel cavity 8 near the position of theexpansion section 30. All other respects the embodiment of FIG. 3 is thesame as the embodiment to FIG. 1. The provision of connection 62 allowscertain advantages, as will be further explained herein.

FIGS. 4 and 4A illustrate another embodiment of a burner apparatus inaccordance with the invention. Burner apparatus 80 includes a refractoryburner block 4, having a plurality of ambient oxidant cavities indicatedat 81 a, b, and c, all feeding a slot 82, and an ambient fuel cavityindicated at 86. The ambient oxidant enters the refractory burner block4 in a first diameter cavity 81 that is narrower in diameter than cavity82. This allows some expansion of the ambient oxidant and the heatedoxidant, the preheated oxidant traversing through a conduit designatedas 84 c in FIG. 4. As perhaps better indicated in FIG. 4A, in thisapparatus, which is a particularly preferred apparatus, there are threepreheated oxidant conduits 84 a, 84 b, and 84 c, positioned within arectangular, slot-shaped cavity 82 in the upper portion of therefractory burner block 4. Tips of the preheated oxidant conduits areindicated as 85 a, b, and c. On the other hand, in this preferredapparatus there are six conduits adapted to convey preheated fuelindicated at 88 a, b, c, d, e, and f, in the lower portion of refractoryburner block 4 and positioned horizontally within cavity 86, with tipsindicated at 87 a and 87 f. The tips of the respective conduits forpreheated fluids are preferably tipped with converging nozzles, andpreferably recessed into burner block 4 an equal distance from therefractory block hot face. Preferably the nozzle exits are positioned ator very near the beginning of respective expansions of their respectiveambient fluid cavity. The distance of recession of the nozzle tips fromthe hot face is preferably from about ¼ to about ½ of the entire lengthof the refractory burner block 4 in this embodiment. Completing theburner apparatus of this embodiment are gasket material 90, preheatedoxidant inlet conduit 92, and preheated fuel conduit 94.

FIG. 5 indicates another preferred embodiment of the burner apparatus inaccordance with the present invention. In this embodiment 70, refractoryburner block 4 comprises a lower half 4 a and an upper half 4 b asindicated in FIGS. 5 and 5A. This design allows for the connection 62 tobe more easily provided for. As illustrated in FIG. 5A, lower half 4 aand upper half 4 b of refractory burner block 4 are fit together along asliding channel 72 which provides a tight fit between the upper andlower blocks. Connection 62 is generally shown as having greaterdiameter near the connection with the cavity adapted to convey ambientoxidant 6, and having a smaller diameter near the connection to thecavity adapted to convey preheated fuel 8. While this is not necessaryfor operation of the burner of this embodiment, this configurationprovides an ejector-type action as will be further explained herein. Thepreheated oxidant and preheated fuel conduits are not shown in theembodiment illustrated in FIGS. 5 and 5A for clarity purposes. A personskilled in the art should understand that these conduits are positionedsimilarly to the embodiment of FIG. 1.

FIG. 6 illustrates a further embodiment 100 of the burner apparatus ofthe present invention which employs a refractory burner block 4 havingan upper cavity 6 formed in an upper portion of the refractory burnerblock. In this embodiment, the refractory burner block is essentiallyhollow on the cold end of the refractory burner block, the hollow regiondefined by an inner surface 5 including a wall that is substantiallyvertical, the wall indicated at 7. The wall is positioned approximatelymidway from the hot face and the cold face of the refractory burnerblock. In this embodiment of the burner apparatus of the invention,provision is made for a metallic burner assembly including components31, 32, 33, 34, and 35. All of these components may be removed from therefractory burner block. Component 31 is merely a metalliccylinder-shaped element adapted to convey ambient fuel. Component 31 isessentially a metallic conduit serving the purpose of cavity 31 in theembodiment FIG. 1. Conduit 34, the conduit adapted to convey preheatedfuel, is a metallic lance which may be removed from the metallic burnerassembly. Conduit 31 is metallic and adapted to convey ambient fuel in aspace defined between an inner surface of conduit 31 and an outersurface of conduit 34. Conduit 32 is a removable, metallic lance adaptedto convey preheated oxidant. Conduit 33 is metallic and adapted toconvey ambient oxidant in a space defined between an inner surface ofconduit 33 and an outer surface of conduit 32. Finally, a connectingconduit 35 serves the purpose of connecting passage as previouslydiscussed in reference to FIGS. 3, 5, and 5A.

The unique construction of the burner apparatus illustrated in FIGS. 6and 6A, illustrates that in this particular embodiment of the burnerapparatus of the invention, one may consider the apparatus to becomprised of two pieces, a refractory ceramic block 4 and a metallicassembly comprised of elements 31, 32, 33, 34, and 35, all of which maybe one or several pieces. Preferably, conduits 31, 33, and 35 are onewelded together and merely inserted into the cavities 6 and 37 ofrefractory burner block 4. Then lances 32 and 34 are preferably clampedor bolted to extensions of conduits 33 and 31, respectively, at the coldend of the burner. This configuration allows easy operator access andmaintenance, and also allows for a myriad of shapes to be envisioned forthe preheated fluid and ambient fluid injection connections.

FIG. 7 illustrates another embodiment of the burner apparatus inaccordance with the invention, showing a burner apparatus 110 having arefractory burner block 4 comprised of an upper half 112 and a lowerhalf 113 separated by the dotted line at 115. The injection of thepreheated oxidant and ambient oxidant is achieved essentially the sameas the embodiment indicated in FIG. 3, however the injection ofpreheated fuel and ambient fuel is somewhat different, with theprovision of the conduit adapted to convey preheated fuel 36 extendingalmost entirely the length of the refractory block 4 to an expansionpoint 31 a which is machined into the refractory burner block lowersection 113. The special feature of the burner apparatus of FIGS. 7 and7A are the provision of a swirl component to the ambient oxidant, or atleast a portion thereof which traverses the connection passage 62. Theambient oxidant which traverses the passage 62 is given atangential-axial momentum which causes the ambient oxidant to swirl inthe cavity 31 and 31 a, causing delayed combustion of the ambient andpreheated fuel. The benefits of this tangential-axial combustion will befurther explained herein. Again, the upper and lower blocks 112 and 113,respectively, are more easily fitted together than a monolithic block.Upper and lower blocks 112 and 113 may be fitted together using thesliding rail assembly indicated in FIG. 5A, which is eliminated forclarity in FIG. 7A.

FIG. 8 is an illustration in schematic format of some of the benefits ofthe burner designs of the present invention. Illustrated is a portion ofa burner apparatus 150 including a portion of the refractory burnerblock 4, and showing a portion of the conduit 36 and its nozzle 38, asillustrated in FIG. 1 for heated fuel. As indicated in FIG. 8, heat flowis generally away from conduit 36 as indicated by the large arrows 152and 154 which is advantageous from the standpoint that ambient fluidwill be somewhat preheated in the burner apparatus and the heat will beused in the combustion process. Furthermore, as the preheated fluidleaves the nozzle indicated at 38, the flow patterns are as indicated bythe arrows at 156, 158, and 160.

The velocity of the preheated fuel leaving the exit nozzle of theconduit adapted to convey preheated fuel ranges from about 5meters/second (m/s) to about 120 m/s, more preferably from about 18 m/sto about 45 m/s. The ambient fuel leaving the burner preferably has avelocity ranging from about 10 to about 220 m/s, more preferably rangingfrom about 15 to about 110 m/s.

The velocity of the preheated oxidant leaving the exit nozzle of theconduit adapted to convey preheated oxidant ranges from about 5meters/second (m/s) to about 60 m/s, more preferably from about 18 m/sto about 27 m/s. The ambient oxidant leaving the burner preferably has avelocity ranging from about 10 to about 90 m/s, more preferably rangingfrom about 15 to about 60 m/s.

The axial distance L_(o) from the exit tip of the preheated oxidantnozzle to the hot face of the refractory burner block (where the ambientoxidant flows out of the refractory burner block and enters thecombustion chamber of the furnace) preferably ranges from about 2 toabout 6 times the inner diameter d_(o) (or equivalent diameter, asdefined previously for “d_(o)”) of the exit tip of the preheated oxidantnozzle. Two adjacent oxidant cavities make a final diverging angle (inthe direction of the flow) between about 0 and 15 degrees, preferablybetween about 0 and 7 degrees.

The axial distance L_(f) from the exit tip of the preheated fuel nozzleto the hot face of the refractory burner block (where the ambient fuelflows out of the refractory burner block and enters the combustionchamber of the furnace) preferably ranges from about 1 to about 3 timesthe inner diameter d_(f) (or equivalent diameter, as defined previouslyfor “d_(f)”) of the exit tip of the preheated fuel nozzle. Two adjacentfuel cavities make a final diverging angle (in the direction of theflow) between about 0 and 15 degrees, preferably between about 0 and 7degrees.

The fuel cavity typically and preferably is matched with a correspondingoxidant cavity in vertical spaced relation in the refractory burnerblock, as seen in the various FIG.s and the discussion herein. Thedistance D_(c) between the central axis of the oxidant cavity and thecentral axis of its respective fuel cavity preferably ranges from about1.0 inches to about 8 inches.

The fuel cavity will preferably have an internal diameter D_(f) rangingfrom about 1.0 to about 6.0 inches, more preferably ranging from about1.84 inches to about 1.16 inches, measured at the exit from the burnerblock. This diameter is, in some embodiments, maintained through theentire length of the fuel cavity. However, it is more preferred tomaintain this diameter only a fraction of the length defined above asL_(f), preferably from about 50 to 90% of that length. The fuel cavitypreferably has a diverging section which transitions the diameter of thefuel cavity from a first diameter to a second, greater diameter,allowing the ambient fuel, and to a certain extent, the preheated fuel,to expand as they traverse through the burner block. In all embodimentsthe internal diameter of the fuel cavity is greater than the outerdiameter of the conduit adapted to convey preheated fuel, or the outermost conduit. In some embodiments there is included a concentric conduitaround the conduit adapted to convey preheated fuel. This concentricouter conduit allows ambient oxidant to travel through an annular spacecreated between the concentric outer conduit and the conduit adapted toconvey preheated fuel.

The oxidant cavity will preferably have an internal diameter D_(o)ranging from about 1.0 to about 8 inches, more preferably ranging fromabout 3.26 inches to about 2.66 inches, measured at the exit from theburner block. The oxidant cavity will typically have a first internaldiameter, and transition into a larger diameter to accommodate anambient oxidant nozzle assembly, which preferably includes an expansionsection allowing for expansion due to preheated oxidant. In allembodiments the internal diameter of the oxidant cavity is greater thanthe outer diameter of the conduit adapted to convey preheated oxidant.

The total quantities of fuel and oxidant used by the combustion systemare such that the flow of oxygen contained in the oxidant ranges fromabout 0.95 to about 1.05 of the theoretical stoichiometric flow ofoxygen necessary to obtain the complete combustion of the fuel flow.Another expression of this statement is that the combustion ratiopreferably ranges from about 0.95 to about 1.05.

The angle “A” between the central axis of the conduit adapted to conveyfuel and the central axis of the conduit adapted to convey preheatedoxidant preferably ranges from about 0 to about 20 degrees, it beingunderstood that this generally causes the fuel to converge toward theoxidant.

The preferred operating temperature ranges of input preheated oxidantand preheated fuel ranges from about 20° C. to about 700° C. and fromabout 20° C. to about 450° C., respectively. More preferable ranges arefrom about 300° C. to about 600° C. and from about 200° C. to about 400°C., respectively. The inventive metallic burner of some embodiments isdesigned such that it can accommodate both cold and hot fluids (fuel andoxidant) for combustion, making it easy to switch from a hot fluidservice to a cold fluid service, or vice-versa.

The present invention discloses several embodiments of preheated fueland/or oxidant combustion burners. The loss of energy due to inert gassuch as nitrogen (contained in air) is overcome by preferably using pureoxygen as an oxidant and preferably natural gas as a fuel. The abovefluids are preferably heated to predetermined temperatures prior toinjection into the inventive burners. The preheating of fuel and/oroxidant is generally achieved by separate dedicated heat exchangersinstalled upstream of the inventive burners, such as those disclosed inapplicant's copending patent application Ser. No. 09/220,559, filed Dec.23, 1998, incorporated by reference herein.

To reduce the energy loss due to nitrogen and for reducing NOxemissions, the burners of the present invention utilize preheated oxygenand/or preheated fuel in the inventive combustion burners.

To avoid any problems with the preheated oxidant initiated metalcorrosion, the preheated oxidant is preferably ducted in metallicconduits made out of alloys or ceramic coated alloys specially designedfor resisting hot oxygen corrosion, such as disclosed in U.S. Pat. No.5,588,974, incorporated by reference herein. Some preferred materialsinclude those known under the trade designations Inconel 600, stainlesssteel 310, Incoloy 800, and PM 2000. Inconel 600 has a composition of(by weight) Ni>72%, Cr 14-17%, Fe 6-10%, C<0.15%, Si<0.5%, and Cu<0.5%.

Some Preferred Alloys Compositions (% by Weight)

Ni Cr Fe C Mn Si Al Ti Others Stainless Steel 310 18-21 22-25 50-52<0.01   1.5 <0.1 — — Mo 3 Incoloy 800 30-35 19-23 >39.5 <0.1  <1.5 <1  0.15-0.6 0.15-0.6 Inconel 600 >72 14-17  6-10 <0.15 <1   <0.5 — — PM200020 Bal. — — — 5.5 0.5 Y₂O₃0.5

Further the alloys may have a ceramic protective surface layer orcoating, the ceramic selected from the group consisting of chromia,alumina, and silica. These may be sprayed onto the alloy surface ornaturally grown in a passivation process from precursors—chromium,aluminum and silicon—diffused into the alloy surface. Preferred arediffused aluminum and silicon. Diffusion coatings lead to surfaceenrichment of Si typically between about 0.2 and 7%, and to surfaceenrichment of Al typically between about 5% to about 40%.

In addition, the inventive burners are constructed to have multipleenclosures. The inner enclosures (conduits) are used for conveyingpreheated fuel and preheated oxygen, whereas the outer enclosures(cavities) are used for conveying ambient temperature fuel or oxidant.The use of outer enclosure having cooler fluid eliminates thermalstresses in the burner body and burner parts remain resilient at hightemperature, unlike ceramics that are very fragile, and resist thermalcycling when switching from cold to hot fluid service.

The inventive burners are designed such that “delayed” combustion isachieved. In the first embodiment, concentric conduit(s) of preheatedoxygen are separated from the natural gas conduit(s) in a specificgeometry such that interaction of preheated oxidant and preheated fueloccurs in the furnace combustion zone.

In the second embodiment, a predetermined portion of ambient oxidant isadmitted in an annular space around an ambient fuel lance and interiorof the fuel burner block cavity. This oxidant amount can range fromabout 5 to about 20% of the total oxygen needed for combustion. Thesmall amount of ambient oxidant allows clean and cool operation withinthe burner block and at the same time intermediate combustion productscomprising soot particles are preferably produced by the preheated fuelcombustion with the ambient oxidant. The intermediate combustionproducts comprising soot is then injected in the furnace for subsequentcombustion with preheated and ambient oxidant mixture.

In the third embodiment, a portion of oxidant (mixture of preheated andambient) is diverted using an ejector effect of the fuel and mixed withthe preheated fuel within the burner block for promoting thermalcracking of fuel and production of intermediate combustion productscomprising soot particles. This is done using a special transportpassage. The intermediate combustion products comprising soot, which israised to higher preheat temperature (due to partial combustion), isthen injected in the furnace. Subsequent combustion takes place with theremaining preheated oxidant in the furnace combustion zone. This burnerembodiment produces a very luminous and low emission flame. The flamealso preferably has lower momentum (compared with the flame produced bythe burner of the first and second embodiments) and it preferablyprovides more uniform heat distribution to the load.

In the fourth embodiment, multiple concentric injector conduits are usedfor both preheated fuel and preheated oxidant to enable higher firingcapability. In this embodiment (FIG. 4) parallel or substantiallyparallel injector conduits for both preheated fuel and preheatedoxidant, preferably form a wide, flat flame. The refractory burner blockgeometry can preferably be constructed from upper and lower halves.Rectangular slots in the hot face are designed for injection of ambientfuel and oxidant.

In a further embodiment, concentric injector conduits use steam as acooling fluid instead of ambient fuel and ambient oxidant. The coolant(steam) can be injected in the furnace via transmission through theannular region between the conduits and their respective cavities. Theadvantage of steam is that it can be compressed in small volume and itis an effective medium for cooling.

The utilization of preheated fuel (preferably at about 400° C.) andpreheated oxidant (preferably at about 600° C.) in the inventivecombustion burners, compared to ambient fuel and oxidant firing intraditional burners, allows an additional fuel and oxidant savings to berealized. In addition, higher furnace productivity (throughput) andlower emissions can be obtained.

Some of the new aspects and various burner details can be summarized asfollowing:

1. In some embodiments, metallic components having multiple enclosuresto enable combustion of preheated fuel and preheated oxidant forobtaining higher thermal efficiency, productivity and lower emissionsfrom a high temperature furnace.

2. A unique concentric burner conduit and nozzle geometry, configurationand construction where the preheated fuel and preheated oxidantinjection, mixing and combustion are achieved for producing a very lowmomentum, high luminosity flame suitable for high temperature heatingapplications. The concentric preheated fuel and preheated oxygenconduits and nozzles allow operation with preheated fluids as well asusing ambient fluids in the case of fuel or oxidant heat exchangerfailure. The conduits, preferably tipped with nozzles, are used forconveying preheated fuel (or oxidant) whereas the outer cavities areused for conveying ambient fuel (or oxidant).

3. A unique burner body construction where the preheated oxidant orpreheated fuel passages are submerged inside a non-preheated oxidant ornon-preheated fuel passages to minimize thermal stresses on variousburner parts. This construction is a multiple enclosure construction.Welding is preferably avoided with the preheated oxidant conduit havingmetallic parts. The parts are assembled using pipe threads, machinethreads (for nozzles) and the supply conduit lances are simply flangedusing high temperature ceramic fiber gaskets for sealing. These multipleenclosure constructions also help in containing any preheated oxidant orfuel leak from the inner (high temperature) enclosure within outerambient (a relatively cooler) oxidant or fuel cavity enclosure,respectively. This leak prevention or containment feature makes thisburner safe and convenient to operate.

4. In addition, the multiple enclosure construction reduces overall heatlosses to the surrounding since colder fuel or colder oxidant is alwaysflowing on the exterior surface of the conduits adapted to conveypreheated gases. This cooler fuel or oxidant is then injected in thefurnace so net heat loss is minimized.

5. Use of heat and corrosion resistant materials: these metals andceramics have been carefully selected for minimum oxidation whilecontinuous exposure to high temperature oxygen.

6. The burner “concentric” conduits for conveying preheated oxidant arepreferably constructed with a metallic alloy that has proven oxidationresistant at high temperature and can withstand thermal cycling—in caseof rapid switching from hot to cold fluid service.

7. New flame characteristics: low NOx, delayed mixing of preheated fuelwith preheated oxidant, and thermal cracking of fuel. Themulti-enclosure burner, bringing preheated fuel and preheated oxidant toburn together, has introduced a new high temperature combustionphenomena that is not commonly found in high temperature meltingapplications.

In one preferred embodiment, the inventive burner comprises a refractoryburner block having an upper half block and a lower half block,so-called split construction. In this embodiment, the upper half blockhas an elongate cavity and conduit therein, the conduit adapted toconvey preheated oxidant, the cavity adapted to convey ambient oxidant.The lower half block has, similar cavity and conduit, the conduitadapted to convey preheat fuel, the cavity adapted to convey ambientfuel. The two halves are preferably matched using standard fasteningtechniques (refractory sliding joints, metallic straps, refractoryplugs, and the like, or any combination of same). This two piececonstruction provides a safe assembly with minimum risk of undesirablecombustion within the interior of the block due to capillary typeleakage of preheated oxidant and preheated fuel through various cracksin the refractory burner block.

8. Backup ambient fuel and ambient oxidant: this backup supply is alwaysthere for rapid switching from hot to cold service, in case ofmalfunction of the upstream heat recovery (or heat exchanger) system foroxidant and fuel preheating. The flow passages for the ambient fuel andambient oxidant are carefully designed such that equivalent flamecharacteristics (flame length, width and momentum) are obtained in termsof preheated or ambient fluid operation. This is achieved byimplementing appropriate flow velocity ranges for both ambient andpreheated fluid operation.

9. A predetermined amount (from about 5 to about 40%) of total oxidantand ambient fuel is used to cool burner parts for reducing thermalstresses and also provide an enclosure for containment of any leaks dueto preheated oxidant or preheated fuel enclosure failure.

10. The conduit adapted to convey preheated oxidant is inserted into itsrefractory burner block cavity in a predetermined angular configuration(0° to 20°) to the conduit adapted to convey preheated fuel. The conduitadapted to convey preheated oxidant is preferably threaded to the oxygensupply pipe and it is preferably equipped with a flexible joint(expansion bellow) to counter thermal expansion and also to easeinsertion into an angular burner block cavity. The burner block cavityfor the conduit adapted to convey preheated oxygen can be at an angle of(0° to 20°) with respect to conduit adapted to convey fuel axis.

11. Both preheated fuel and preheated oxidant are injected in two“concentric streams,” the cooler fluid surrounds the hotter fluid: thisis a safety aspect of the design; burner parts are cooled down on theexterior body to minimize thermal stresses and heat losses to thesurrounding.

12. Cooler burner body: because of the cold fluid surrounding the hotone, an insulating layer is formed that keeps the refractory burnerblock body at lower temperatures; moreover, an insulating sheath coversthe burner external parts, ensuring their handling is not dangerous tooperators.

As previously explained, illustrated in FIG. 1, both preheated fuel andoxidant conduits and nozzles are concentric and the combustion burnerhas multiple enclosures. The preheated fluid (fuel and oxidant) conduitsare submerged in ambient fluids. All preheated fluid metallic parts areeither threaded or flanged. Welding is preferably avoided with themetallic parts. The ambient fluids (fuel and oxidant) are used forcooling refractory internal surfaces and also external surfaces of theconduits adapted to convey preheated fluids and their nozzles, as wellas the burner manifold. In this way the whole burner remains at atemperature preferably no higher than 300 to 400° F. without externalinsulation. By using external insulation, the refractory block outerbody temperature can be maintained around 150 to 200° F.

The various particularly preferred design velocities for fuel andoxidant at the concentric nozzle exit are given in Table I. The low andhigh range are given to suit various flame characteristics, such asshort and bushy to long and lazy flame. The preheated fuel and oxidantvelocities are achieved by using a standard straight internal diameternozzle with slight taper on the exterior (see FIG. 1). The nozzlespreferably have coarse machine threads so they can be removed orinstalled quite easily. The amount of ambient fuel and ambient oxidant(as a fraction of total fuel) are selected such that the inventiveburner preferably operates in “cold conditions” (without preheatedfluids) with the same nozzles. The cross sectional annular area betweenthe exterior of the conduits adapted to convey preheated fluid and theburner block internal cavity diameter determines the ambient fluid flowvelocities.

TABLE I Ambient and Preheated Fuel and Oxidant Velocities andProportions Ambient Ambient Preheated Preheated Nat. Gas Oxygen Nat. GasOxygen Low Range (ft/sec)  30  30  15  15 High Range (ft/sec) 750 300400 200 Volume (% of total) 0 to 50 0 to 50 50 to 100 50 to 100Preheated Operation Volume (% of total) 100 100  0  0 Cold Operation

The preheated oxidant velocity preferably does not exceed 400 ft/sec atthe exit of the nozzle to avoid faster oxidation of nozzle material.However, burners constructed to achieve preheated oxidant velocity ofthis high nature can be within the invention, as long as the velocity istemporary or cyclic in nature. The conduits adapted to convey preheatedoxidant are preferably constructed of nickel-chromium-iron alloy andinternal flow velocities are preferably kept below 100 ft/sec to reducehigh temperature oxidation of the conduit material. The ambient oxidantvelocities are limited to maximum of 150 ft/sec in the annular regionbetween the conduit adapted to convey preheated oxidant and its cavity,and maximum velocity at the nozzle is about 750 ft/sec. The desiredvolumetric proportions of both ambient and preheated fluids for“standard” preheated operation and “backup” cold operation are alsolisted in Table I.

As illustrated in FIG. 1, the “concentric” preheated and ambient fuelnozzle(s) is preferably installed substantially horizontally, whereasthe “concentric” preheated and ambient oxygen nozzle(s) is preferablyinstalled at an angle A=±20° to the axis of the preheated fuel conduit.The preferred angle is about 10° downward to the horizontal axis. Theaxial spacing of concentric oxidant nozzle (L_(o)) and concentric fuelnozzle (L_(f)) from the burner block hot-face preferably ranges fromabout 2 inches to about 8 inches. This distance is based on overallburner block length and the furnace wall thickness.

FIG. 2 illustrates the second embodiment where from about 5 to about 20%of the oxygen required for stoichiometric combustion is admitted, atambient temperature, in the annular passage around the conduit adaptedto convey ambient fuel exterior and interior of the fuel burner blockcavity. The ambient oxidant keeps the burner block interior clean, cooland at the same time it provides sufficient oxygen to crack at least aportion of the preheated and ambient fuel (into soot particles) due topartial combustion in the burner block cavity. The velocity ranges ofvarious fluids remain same as in the first embodiment. The combustion ofsoot-rich preheated fuels in the furnace with preheated oxidant producea very luminous and low NOx emission flame.

In the third embodiment, illustrated in FIG. 3, a minor portion ofambient oxidant is directed toward the preheated fuel nozzle exit via aspecial passage in the burner block. The minor portion of the ambientoxidant stream is effectively entrained by the ejector action of theambient and preheated fuel jets. The low-pressure region around thepreheated fuel jet in the burner cavity is sufficient to withdraw fromabout 5 to about 20% of total oxidant (mixture of preheated and ambient)in the special passage downward and it is directed towards preheatedfuel jet. Here the fuel and oxidant mix and produce soot particles andhigher hydrocarbons. The combustion of higher hydrocarbons in thefurnace with preheated oxidant produces a very luminous and low emissionflame.

FIG. 4 illustrates the fourth embodiment having individual rectangularslots for the ambient fluids (both fuel and oxidant) and having multipleconduits adapted to convey preheated fuel and oxygen. The rear of theburner has separate manifolds for ambient fuel and ambient oxidantsupply. In this manifold, which is preferably rectangular in shape,several conduits adapted to convey preheated fuel are inserted andsecured using standard flange connections in the rear of the burner.This embodiment is similar to the first embodiment except multipleconduits adapted to convey preheated fluids are positioned (side byside) in a rectangular manifolds, the manifolds adapted to conveyambient fluids.

The rectangular slots (width and height) are preferably sized to givethe same ambient fluid velocity ranges as indicated in Table I. Themultiple conduits adapted to convey preheated fluids are sized accordingto Table I specifications for velocities and volume proportions. It ispreferred that all conduits produce the same flow rate and velocity, butthis is not required. This approach will allow firing large capacities(as high as 30 MM Btu/hr) and oxidant preheat temperatures as high as700° C. and fuel preheat temperatures as high as 400° C.

The fifth embodiment employs “dry steam” as a cooling media instead ofambient fuel and ambient oxygen. The steam keeps the burner externalenclosures clean, cool, and at the same time it prevents any thermalstresses on the burner body. The steam is then injected in the furnace.This particular embodiment can be applied to all embodiments byreplacing ambient fuel and ambient oxygen with steam.

Additional features of the invention include the use of fuel oils in theinventive burners. Liquid fuels such as diesel, #4, #6, bunker type canbe used. The heavier fuel oils (such as bunker C) are generallypreheated up to about 200° C. and are inserted into the preheated fuelport using an atomizer unit, such as that described in U.S. Pat. No.5,984,667, incorporated herein by reference.

The use of the split burner block in some embodiments allows some of theambient oxidant to be ejected into the fuel stream. This is generallynot achievable using a monolithic burner block. One solution is the useof two individual blocks, one for oxidant and one for fuel, where thecold oxidant channel connecting them is properly machined, and that havecomplementary shapes to assemble with one another in a sealed manner.The example illustrated in FIGS. 5 and 5A illustrates the “slidingrails” design, which is easy to fit together and achieve good seal.

An additional technical solution for the inventive burner is to envisionthe burner as having two functional parts; first, the part whichincludes the hot face (which is exposed to the furnace radiation) whichserves the role of a thermal insulation. Here the aim is to prevent thefurnace heat losses and the overheating of the parts accessible to theoperator. Therefore, the hot face preferably comprises refractorycompounds molded and/or machined as illustrated in FIG. 1. Suitablematerials for the refractory burner block include fused zirconia, fusedcast AZS (Alumina-Zirconia-Silica), rebonded AZS, or fused cast alumina.The choice of a particular material is dictated by, among other things,the type of furnace or heating system the burner is used for. Second,the part of the burner that includes the cold face, the side that thefurnace operator has access to install or remove the burner. In thispart the primary function is mechanical. It has to support andaccommodate the fuel and oxidant metallic conduits. The mechanicalfunction is preferably fulfilled by employing a metallic body, which hasthe advantage of being able to be constructed into complex shapes thatceramic blocks cannot be constructed with. Thus, the conduit adapted toconvey ejected ambient oxidant from the ambient oxidant cavity to theambient fuel cavity can be an integral component of this metallic body.

For increased thermal insulation, the space between the metallicconduits can be plugged with some fibrous insulation, such as glassfibers. A lining made thereof can be inserted between the back of therefractory ceramic part of the burner and the metallic flange connectingthe metallic body part to the refractory part of the burner. Theconnection between the metallic parts and the refractory ceramic blockpart is preferably sealed by a tight contact between metal and ceramicinside the block, and a proper compression gasket at the rear of therefractory ceramic block. Entrainment caused by the fluids flowing intothe furnace prevents any accumulation of oxidant or fuel inside thehollow burner block.

A carburization resistant sleeve is preferably used as part of theconduit adapted to convey preheated fuel, near the fuel nozzle. Sincepreheated fuel could cause too much carburization of a metallic sleeve,it is preferable to use materials selected from the group consisting ofgraphite, silicon carbide (SiC), alumina (Al₂O₃), and the like, orcombination of those materials. The carburization resistant materialpreferably also has a fair oxidation resistance, because of theimpingement of ambient oxidant through the conduit connecting theambient oxidant conduit with the ambient fuel conduit.

A swirling motion may be introduced in the ambient oxidant flow. The useof a metallic interconnect passage between the ambient oxidant andambient fuel cavities offers flexibility to use complex shapes formetallic channels between the oxidant and fuel cavities. In onepreferred embodiment, the ambient oxidant is ejected around thepreheated fuel stream in a tangential-axial direction as illustrated inFIG. 7A (in contrast to radial ejection illustrated in FIGS. 5 and 5A).This tangential-axial oxidant injection produces a swirling oxidantstream, which is beneficial to the flame in several ways. The swirlingin the outer oxidant annulus is known to produce additional soot due tothe higher residence time, and delay mixing between fuel and remainingoxidant and thus delay combustion; a slower combustion then leads tolower peak flame temperatures inside the flame structure and anincreased flame length. In the meantime, the recirculation of exhaustgases into the flame could reduce the Nox emissions level and possiblyinduce higher flame luminosity.

Process Advantages Due to Concentric Nozzle Design

The concentric nozzle design for both preheated fuel and oxidantconduits and nozzles has distinct advantages as far as combustionprocess and heat transfer are concerned. This is illustrated in FIG. 8.

As illustrated in FIG. 8, the concentric jets having the preheated fluid(fuel or oxidant) in the center and ambient fluid on the outside preventany diffusion of preheated fluid into refractory burner block. Therefractory burner block internal surfaces generally have porous surfacesand small cracks due to thermal cycles. By having a concentricconstruction, the preheated fluid is well contained inside a metallicenclosure whereas the cooler fluid is contained inside the refractoryenclosure (in the burner block). As illustrated, the ambient fluid coolsthe preheated fluid conduit and the burner block interior by forcedconvection.

FIG. 8 also illustrates that by combining both velocity profiles (ofpreheated fluid and ambient fluid), a much wider impact area is obtainedin the furnace with concentric conduit design. This has positiveimplications as far as combustion is concerned. The wider overall jetallows more surface area for flame development and much wider heatrelease, resulting in lower peak flame temperatures and more uniformheat distribution.

Another advantage of concentric conduit design is active cooling ofpreheated fluid conduit material and resulting lower operatingtemperature of the material. This results in lower oxidation/corrosionrate and longer life of the combustion burner.

The preheated fuel and oxidant are injected through “concentric” burnernozzle(s) for creating oxy-fuel combustion inside the heating furnaceatmosphere. The oxidant and fuel are preheated to high temperature (˜400to 1800° F.), preferably via a heat exchanger, are conveyed through amulti-enclosure-self-cooled burner body, self-cooled burner nozzles(s)and finally into a special refractory burner block. In one embodiment,both preheated oxidant and fuel prior to injection in the heatingfurnace react partially inside the refractory block cavity to promotethermal cracking of gaseous fuel to produce higher hydrocarbon speciesand soot particles. The subsequent combustion of soot rich, preheatedfuel and preheated oxidant in the furnace atmosphere produce a veryluminous and low emission flame. The configuration of burner nozzle(s)is such that it promotes thermal cracking of fuel, delayed mixing,enhanced flame radiation and lower emissions of NOx and processparticulate. Preferred materials for the “concentric” oxidant and fuelnozzle(s) are nickel-chromium-iron alloys, or ceramic coated temperatureresistant stainless steels. The burner is able to switch from hotoxidant and fuel service to ambient oxidant and fuel service veryeasily.

Having described the present invention, it will be readily apparent tothe artisan that many changes and modifications may be made to theabove-described embodiments without departing from the spirit and thescope of the present invention.

What is claimed is:
 1. A burner apparatus comprising: a) a conduitconveying a preheated oxidant flow and having outlet and inlet ends; b)a conduit conveying a preheated fuel flow and having outlet and inletends, the conduit conveying the preheated fuel flow being substantiallyparallel to the conduit conveying the preheated oxidant flow, theconduit conveying the preheated oxidant flow being positionedsubstantially vertically above the conduit conveying the preheated fuelflow; c) the conduit conveying the preheated oxidant flow beingpositioned within a respective elongate cavity in a refractory burnerblock, the conduit conveying the preheated fuel flow being positionedwithin a respective elongate cavity in the refractory burner block, eachof said conduits positioned in their respective cavity such that asubstantially annular region is present between an outer surface of eachsaid conduit and respective cavity; and d) each conduit inlet endextending through a respective plenum and receiving an ambienttemperature fluid flow, the plenums adapted to pass said ambienttemperature fluid flow into the respective annular regions, wherein theflows of preheated fuel and preheated oxidant through the respectiveconduits occur simultaneously with the flow of the ambient temperaturefluids through the respective cavities.
 2. Burner apparatus inaccordance with claim 1 wherein the outlet end of each cavity iscoterminous with a hot face of the refractory burner block.
 3. Burnerapparatus in accordance with claim 1 wherein a plurality of conduitsconveying the preheated oxidant flow are positioned in respectivecavities in the refractory burner block, and plurality of conduitsconveying the preheated fuel flow are positioned in respective cavitiesin said refractory burner block.
 4. Burner apparatus in accordance withclaim 1 wherein the outlet end of the conduit conveying the preheatedoxidant flow is connected to an outlet of a preheated oxidant nozzleassembly, the preheated oxidant nozzle assembly comprising an expansionjoint which connects an inlet of the preheated oxidant nozzle assemblyto a preheated oxidant nozzle downstream of the expansion joint, thepreheated oxidant nozzle having a preheated oxidant nozzle outlet and anaxis.
 5. Burner apparatus in accordance with claim 4 wherein thepreheated oxidant nozzle outlet is recessed from the outlet end of thecavity in which is positioned the conduit conveying the preheatedoxidant flow.
 6. Burner apparatus in accordance with claim 4 wherein theoutlet end of the conduit conveying the preheated fuel flow is connectedto an inlet of a preheated fuel nozzle, the preheated fuel nozzle havinga preheated fuel nozzle outlet and an axis.
 7. Burner apparatus inaccordance with claim 6 wherein the preheated oxidant nozzle axis isangled toward the fuel nozzle axis.
 8. Burner apparatus in accordancewith claim 7 wherein the preheated fuel nozzle outlet is recessed fromthe outlet end of the cavity in which is positioned the conduitconveying the preheated fuel flow.
 9. Burner apparatus in accordancewith claim 1 wherein the cavity in which is positioned the conduitconveying the preheated fuel flow or the cavity in which is positionedthe conduit conveying the preheated oxidant flow comprises an expansionsection, the expansion section connecting a first ambient fluid cavitypositioned upstream of the expansion section and a second ambient fluidcavity positioned downstream of the expansion section and having aninternal diameter greater that an internal diameter of the first ambientfluid cavity, the expansion section having an inlet and an outlet, theinlet of the expansion section having a diameter less than the outlet ofthe expansion section.
 10. Burner apparatus in accordance with claim 9wherein the conduit conveying the preheated fuel flow terminates with anozzle, the nozzle having a nozzle outlet that is positioned coterminouswith the inlet to the expansion section of its respective fluid cavity.11. Burner apparatus in accordance with claim 1 wherein the conduitconveying the preheated fuel flow extends through and is positionedwithin an intermediate conduit, the intermediate conduit positionedbetween the conduit conveying the preheated fuel flow and its respectivecavity, the intermediate conduit having an outlet and an inlet end, theintermediate conduit inlet end connected to one of said plenumsreceiving ambient fuel, the intermediate conduit and said cavitycreating an annular region for introduction of ambient oxidant, theintermediate conduit and the conduit conveying the preheated fuel flowcreating an annular region for conveying ambient fuel.
 12. Burnerapparatus in accordance with claim 1 wherein further including a fluidconnection which connects the cavity in which the conduit conveying thepreheated oxidant flow is positioned with the cavity in which theconduit conveying the preheated fuel flow is positioned.
 13. Burnerapparatus in accordance with claim 12 wherein said fluid connection hasa fluid connection inlet and a fluid connection outlet, the fluidconnection inlet connected with the cavity in which the conduitconveying the preheated oxidant flow is positioned at a positionupstream of a point where the fluid connection outlet is connected tothe cavity in which is positioned the conduit conveying the preheatedfuel flow.
 14. Burner apparatus in accordance with claim 13 wherein therefractory burner block is comprised of an upper refractory burner blockand a lower refractory burner block, the upper and lower refractoryblocks contacted in a plane which is generally parallel with an axis ofthe conduit conveying the preheated fuel flow, the lower refractoryburner block having positioned therein the cavity in which is positionedthe conduit conveying the preheated fuel flow, and the upper refractoryburner block having positioned therein the cavity in which is positionedthe conduit conveying the preheated oxidant flow.
 15. Burner apparatusin accordance with claim 1 wherein the conduit conveying the preheatedoxidant flow is an alloy selected from the group consisting of: a) analloy comprising (by weight) Ni>72%, Cr 14-17%, Fe 6-10%, C<0.15%,Si<0.5%, and Cu<0.5%; b) an alloy comprising (by weight) 18-21% Ni;22-25% Cr; 50-52% Fe; C<0.1%; 1.5% Mn; Si<0.1%; and 3% Mo; c) an alloycomprising (by weight) 30-35% Ni; 19-23% Cr; Fe>39.5%; C<0.1%; Mn<1.5%;Si<1%; 0.15-0.6% Al; 0.15-0.6% Ti; and d) an alloy comprising (byweight) 20% Cr; 5.5% Al; 0.5% Ti; 0.5% Y₂O₃; balance Fe.
 16. Burnerapparatus in accordance with claim 15 wherein the alloys have a ceramicprotective layer or ceramic coating, the ceramic selected from the groupconsisting of chromia, aluminum, and silica.
 17. Burner apparatus inaccordance with claim 15 wherein the alloys have been diffusion or spraycoated.
 18. Burner apparatus in accordance with claim 17 wherein thediffusion coating leads to surface enrichment of Si typically betweenabout 0.5 and 5%, and to surface enrichment of Al typically betweenabout 20% to about 35%.
 19. Burner apparatus in accordance with claim 6,wherein; a) each of the preheated oxidant nozzle outlet and thepreheated fuel nozzle outlet are spaced from the hot face of therefractory burner block by a same distance.
 20. Burner apparatus inaccordance with claim 6, wherein: a) the preheated oxidant nozzle outletis spaced from the hot face of the refractory burner block by a distanceL_(o); b) the preheated fuel nozzle outlet is spaced from the hot faceof the refractory burner block by a distance L_(f), and c) L_(o) is notequal to L_(f).
 21. Burner apparatus is accordance with claim 12,wherein: a) the preheated fuel flow flows along a vector V_(f), b) thepreheated oxidant flow flows along a vector V_(o); and c) the fluidconnection diverts at least a portion of the preheated oxidant flowalong a vector V_(c) that does not lie within a plane defined by vectorsV_(f) and V_(o).
 22. Burner apparatus in accordance with claim 12,wherein: a) the fluid connection imparts a swirling motion to thepreheated oxidant flow flowing therethrough.
 23. A burner apparatuscomprising: b) a plurality of conduits conveying a flow of preheatedoxidant each having outlet and inlet ends and being aligned in a firstplane; c) a plurality of conduits conveying a flow of preheated fueleach having outlet and inlet ends being aligned in a second plane, thefirst plane being parallel to the second plane; d) each of the conduitsis positioned within a respective one of a plurality of elongatecavities in a refractory burner block, each of said conduits positionedin the respective cavity such that a substantially annular region isdefined between an outer surface of each said conduit and the respectivecavity; and e) each conduit inlet and extending through a respectiveplenum receiving a flow of ambient temperature fluid, the plenumspassing said ambient temperature fluid into the respective annularregions, wherein the flows of preheated fuel and preheated oxidantthrough the respective conduits occur simultaneously with the flow ofthe ambient temperature fluids through the respective cavities.
 24. Aburner apparatus, comprising: f) a burner assembly comprising, i) afirst conduit having an inlet and an outlet, ii) a second conduitconveying a flow of preheated oxidant extending at least partly throughsaid first conduit such that a first annular region is defined betweenan inside surface of said first conduit and an outside surface of saidsecond conduit, said first annular region conveying a flow of ambientoxidant, iii) a third conduit having an inlet and an outlet, iv) afourth conduit conveying a flow of preheated fuel extending at leastpartly through said third conduit such that a second annular region isdefined between an inside surface of said third conduit and an outsidesurface of said fourth conduit, said second annular region conveying aflow of ambient fuel, and v) a fifth conduit in fluid communication withsaid first and second annular regions and conveying at least a potion ofsaid flow of ambient oxidant from said first annular region to saidsecond annular region; and b) a refractory burner block having a hotface and a cold face, said refractory burner block having a hollowvolume extending from said cold face to a position within saidrefractory burner block intermediate to said cold face and said hotface, said intermediate position defined by a wall of a substantiallysolid portion of said burner block, said substantially solid portionhaving a first cavity adapted to receive said flow of preheated oxidantfrom said second conduit, and a second cavity adapted to receive saidflow of preheated fuel from said fourth conduit, wherein said flows ofpreheated oxidant, ambient oxidant, preheated fuel and ambient fueloccur simultaneously during operation of said burner apparatus. 25.Burner apparatus in accordance with claim 24 wherein said conduitsconveying the preheated oxidant and preheated fuel flows are bothmetallic and both removable from the metallic fluid flow assembly.